47:1 · Yet another of humankind's earliest ideograms. It has been found, among other places, on ancient rock paintings in the inner Sahara. It has also been used in many of the earliest systems of writing.
    In alchemy, it was used as a sign for spiritus, the spirit, that is the essence, the finest, the most precious. Alcohol, for example, was the spirit in wine. Spiritus, or spirit was also drawn and .
    In early astronomy represented the sun's center. In a geological context means a flat, grooved rockface. (If the sign appears with an arrow, as , it denotes the direction of the movement of the ice flow that grooved the rock.)
    In modern times the most common use of this extremely ancient ideogram is in technical contexts, where one of its most common meanings is (open) valve.
    On ships' sides it is a main part of the Plimsoll mark (see in Group 53).
    On cameras it is sometimes used to indicate the focal plane or film plane. Compare with , which stands for focus.